The field of the invention relates to refractory compositions for sintered refractory articles formed with predominantly grain of fused AZS (alumina-zirconia-silica) material, particularly fusion-cast AZS refractory solidified and cooled as a unitary mass or block in a relatively slow manner and thereafter crushed into grain to be rebonded.
The general concept of rebonding crushed fused AZS grain was apparently first disclosed in U.S. Pat. Nos. 1,240,490 and 1,240,491. The rebonding was to be accomplished by ordinary ceramic bonds (cf. the clay-flux bond in U.S. Pat. No. 930,376). For refractories, it was noted that the fused AZS composition could contain zirconia up to equimolecular proportion with alumina (ca. 54.7 wt.% ZrO.sub.2 and 45.3 wt.% Al.sub.2 O.sub.3 when ignoring impurities).
A somewhat similar teaching is presented in U.S. Pat. No. 1,324,546 although the composition of the fused AZS grain apparently includes a substantial amount of MgO. Besides the fused grain and clay-flux bond, it is noted that finely ground unfused materials of the same composition as the fused grain may also be added. The refractory products are said to have resistance to corrosive and erosive action of molten material (e.g. molten metals or glass) in contact therewith, to deformation at high temperature and to cracking during changes of temperature.
It was later recognized that the clay-flux bonds of those early rebonded fused AZS grain refractories significantly limited refractoriness and resistance to chemical action. As a result, efforts were made, as noted in U.K. Pat. Nos. 605,215 and 610,334, to form rebonded refractories solely of fused AZS grain, initially with normal fusion-cast material and then with rapidly cooled grain formed by dispersing a melt into droplets, or of fused AZS grain combined with another fused grain where the glassy phase of one was more refractory than the glassy phase of the other. However, no apparent special effort was made to control particle sizing other than to provide a mixture of granules and fine particles.
In more recent times, several particular compositions have been developed for producing refractory articles with rebonded fused AZS grain for resisting contact action of molten materials and thermal shock. Each one requires a different special combination of materials for proper attainment of suitable properties. U.S. Pat. No. 3,567,473 prescribes mixing certain fused AZS grain with either tabular alumina plus alpha quartz or kyanite as well as with calcined alumina, magnesium oxide and colloidal silica, each in particular proportions. U.S. Pat. No. 3,782,980 prescribes mixing certain fused AZS grain with an essential proportioned combination of zircon (or zirconia) and alumina. U.K. Pat. No. 1,429,723 prescribes combining certain fused AZS grain with alumina and/or mullite together with some silica binder. U.S. Pat. No. 3,846,145 prescribes certain fused AZS grain to be combined with kyanite, zircon, calcined alumina, chromic oxide and silica.
It has also been proposed in U.K. Pat. No. 1,254,792 to provide a binder (or mortar) of fusion-cast AZS grain mixed with either hydraulically setting cement, expanded clay or chemical binder to join relatively small fusion-cast slabs together to form a composite refractory block.
None of these prior art rebonding compositions are seen to comprehend the unique balanced combination refractory composition of the invention disclosed and claimed herein, which is believed to provide superior properties to those of these prior art compositions.